Stratigraphy,depositional environment,and cultural significance of holocene sediments in patterned wetlands of central Veracruz,Mexico

The coastal wetlands of Veracruz State, Mexico contain many areas of rectilinearly patterned ground. These are the remains of Prehispanic agricultural complexes. Reconnaissance-level stratigraphic studies were carried out in one such wetland area, the “San Juan Basin,” in order to reconstruct the local environmental history. Basal, well-sorted fine sand, which underlies the basin, was likely deposited in the intertidal and beach zones as marine waters gradually left the San Juan Basin. Progradation of the Rio La Antigua delta on the north and the development of coastal dunes on the east closed the embayment by the mid-Holocene. Thereafter, large volumes of silt and clay were deposited in the basin, in large part during the annual floods of the La Antigua River and other streams. Prehispanic inhabitants dug drainage canals and cultivated the seasonally emergent surface leaving behind artifacts, charcoal, and microfossils of maize. The cultivation destroyed original sedimentary structures and converted the naturally deposited sediment to a massive dark gray silty clay. After the fields were abandoned, they were covered by brown silty peat, but the canals and platforms are still detectable on the surface.